Compact binoculars for nighttime vision

ABSTRACT

Compact binoculars for nighttime vision with a center of gravity close to the user. The binoculars have an optical architecture with an inclined principle pathway. The principle pathway extends by way of a first eyepiece pathway with a second eyepiece pathway branching in a different direction. The binoculars include a bent entrance objective conjugate with a light intensifier tube forming an image of a scene along a viewing axis. The image is next transmitted on the two eyepiece pathways to two eyepieces by way of an optical splitter. The splitter partially transmits the flux to a first eyepiece pathway inclined with respect to the plane of the eyepieces and on a second eyepiece pathway which has an axis lying in the plane perpendicular to the viewing axis and passing through the axis of the principle pathway.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to nighttime vision, that is to say theobservation of a scene under very weak conditions of illuminationprovided for example by starlight or moonlight, and without additionallighting of the scene.

DISCUSSION OF THE BACKGROUND

Nighttime vision systems are designed to be carried in the hand or toallow hands-free use. In the latter case, the vision system is fixed tothe user's face with the aid of a support mask fitted with straps or ona vehicle as is the case for example in respect of infrared periscopesof the type described for example in the GB Patent 918213.

Vision devices carried in the hand are principally intended for distantobservation and incorporate an optical combination capable of multifoldmagnification of the observed field. On the other hand, nighttime visionsystems of the hands-free type, intended for movement, vehicle drivingor the carrying out of nighttime work, exhibit a magnification equal toone so as to offer natural conditions of vision. The invention isparticularly, but not exclusively, intended for this type ofapplication.

Nighttime vision systems are conventionally based on employing an imageintensifier tube, including a photocathode serving as entrance surface,a microchannel electron transfer and multiplication system, and aphosphor screen serving as exit surface. A wide-aperture objective formsan image of the observed scene on the entrance surface, then the imageis electronically intensified and finally restored on the phosphorscreen so as to be observed through an eyepiece assembly.

Two-eyepiece vision is obtained by separating the flux exiting the tubeinto two eyepiece pathways with the aid of an optical splitter.

The need to fix night driving equipment to the head gives rise to thepresence of significant ergonomic constraints. Thus, the mass of theequipment and its protuberant shape, owing to the alignment of theelements--objective, tube, eyepiece--on a viewing axis, give rise to ashift of the center of gravity of the head and modify its inertialcharacteristics, this causing problems of fatigue in the neck region.Moreover, the presence of this fragile and relatively long protuberance(conventionally between 100 and 170 mm) reduces the mobility of theuser, especially in respect of movements under difficult conditions orin respect of vehicle driving.

To solve this problem, there is known from U.S. Pat. No. 4,826,302 abent optical system in which the objective and the intensifier areoriented along a horizontal axis perpendicular to the viewing axis. Thedimension of the equipment along the viewing axis is thereby reduced andthe center of gravity of the assembly is shifted towards the observer.However, this design requires that a significant number of reflectionsbe employed on each of the optical pathways.

SUMMARY OF THE INVENTION

The invention aims to obtain even more compact nighttime visionbinoculars employing a reduced number of optical elements.

To achieve these objectives, the invention is based on setting up aprincipal optical pathway inclined with respect to the plane of theoptical axes of the eyepieces and culminating in a first eyepiecepathway onto which will be grafted a second eyepiece pathway.

More precisely, the subject of the invention is binoculars for nighttimevision including an entrance objective conjugate with alight-intensifier tube for forming an image of a scene from light fluxoriginating from the scene along a viewing axis, an intensified imagenext being transmitted by an image transport and by an optical splitterwhich partially transmits the flux by transmission and reflectionrespectively on a first pathway to a first eyepiece and on a secondpathway, which is bent twice, to a second eyepiece, the eyepieces havingaxes parallel to the viewing axis, characterized in that the tube andthe image transport are aligned so as to constitute a principal opticalpathway along a principal optical axis lying in a plane perpendicular tothe viewing axis and inclined with respect to the plane of the axes ofthe eyepieces, in that the second eyepiece pathway, which is bent twiceand which has an axis lying in the plane perpendicular to the viewingaxis and passing through the axis of the principal pathway. According toa first example embodiment, the transmission of flux is carried out withthe aid of an image transport optic composed of a first element locatedbetween the tube and the splitter and of a second element located oneach of the eyepiece pathways. This optical combination therefore formstwo image transport optics, one transport by transmission through thesplitter and one transport by reflection on the separator, respectivelyon the first and the second eyepiece pathway. Each image transport formswith the conjugate eyepiece an eyepiece assembly, preferably of themicroscope type.

Advantageously, the transmission of the flux on the second eyepiecepathway is carried out either with the aid of optical elementsconstituting a single image transport coupled to two roof prisms, orwith the aid of two image transports coupled to two plane reflectors. Anoptic of the magnifying glass type which directly recasts the image fromthe screen of the tube.

According to a second example embodiment, the intensifier tube has imageinverter fibres. Advantageously, the roof prisms of the second eyepiecepathway are then replaced by plane reflectors. Moreover, thetransmission of the flux on the first eyepiece pathway constituting anoptic of the magnifying glass type which directly recasts the image fromthe screen of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will emerge on reading thefollowing description accompanied by the appended figures whichrespectively represent:

FIG. 1, a first example embodiment of the nighttime vision binocularsaccording to the invention;

FIG. 2, a second example embodiment of the binoculars according to theinvention.

DISCUSSION OF THE PREFERRED EMBODIMENTS

The first example embodiment, illustrated by FIG. 1, shows the basicarrangement proposed by the invention: a principal optical pathway withaxis XAOBX', bent at A and B and hinged about three axes, the viewingaxis AX of the binoculars, the optical axis AB of revolution of thelight intensifier 2, and the optical axis BX' of a first eyepiece 3, ofthe eyepiece for the left eye in the example illustrated. An entranceobjective 1 can be disposed either on the viewing axis AX or on the axisof the tube 2. It can also, as illustrated, be composed of two elements1_(a) and 1_(b), the first being located on the viewing axis AX and thesecond on the axis of the tube 2.

The objective and the eyepiece are bent, respectively:

at A with the aid of a plane reflector 4 disposed between the entranceoptical elements 1_(a) and 1_(b) then constituting a bent objective;

at B with the aid of a second plane reflector 5, parallel to the firstreflector 4, so that the two reflectors form a rhombohedron, the opticalaxis BX' of the eyepiece then being parallel to the viewing axis AX.

Between the light intensifier 2 and the eyepiece 3 there is ,provided anoptical combination with image transport for transmission of the lightflux originating from the observed scene. In this first exampleembodiment, this image transport is composed of two optical elements 6and 7, the optical elements 6 and 7 and the eyepiece 3 being opticallycomputed so as to form for example an eyepiece assembly of microscopetype, that is to say with formation of an intermediate image.

In order to constitute a second eyepiece optical pathway going to theother eye, the right eye in the case of the example illustrated, thereis provided at the point 0 of the central span AB of the principalpathway, an inclined pathway splitter 8 which diverts half of theincident light flux to a second eyepiece 9, in this instance theeyepiece for the right eye.

Two eyepiece pathways are thus created onwards of the splitter 8: afirst eyepiece pathway with axis OBX', for the left eye in the exampleillustrated in FIG. 1, and a second eyepiece pathway with axis OCDY forthe right eye.

The first eyepiece pathway, consisting of the image transport 6, 7 andthe eyepiece 3, extends the principal pathway and the light flux istransmitted partially on this pathway through the pathway splitter. Thesecond pathway is followed by the light flux reflected by the splitter8.

In order to transmit the light up to the second eyepiece, the secondeyepiece pathway includes an image transport optic: for example, opticalelements 10 and 11 are placed between the splitter 8 and the secondeyepiece 9 and are computed such that the optical elements 6, 10 and 11constitute a single image transport optic. The image transport 6, 10, 11likewise forms, with the eyepiece 9, a microscope type eyepieceassembly. Under these conditions, the two eyepiece pathways each consistof an image transport having a common element, the element 6 and of aneyepiece.

The term "optical element" used in this description signifies optical orlens group composed of a suitable number of thin lenses (at least one)whose geometrical and optical characteristics are computed so as toobtain the desired optical effects (convergence, correction of opticalaberrations). The optical computation comes within the know-how of thoseskilled in the art.

The secondary optical pathway which will be grafted at the point 0 ontothe principal optical pathway X'OX has in the example embodiment,onwards of the pathway splitter 8, an optical axis OCDY likewise benttwice about three spans. The optical axis of the second eyepiece 9,which coincides with the span DY of the secondary optical pathway, isparallel to the optical axis BX' of the first eyepiece 3. Under theseconditions, the axes of the eyepieces BX' and DY are parallel and arealigned with the axes of vision of the eyes of the observer Y1 and Y2.The axes BX' and DY thus define a reference plane of vision for theuser, in general horizontal.

To obtain correct orientation of the image exiting the eyepieces, theintensifier is a tube without image inversion.

In the example embodiment illustrated, the first optical bend C of thesecond eyepiece pathway is produced with the aid of a roof prism 12,located between the two elements 10 and 11 of the image transport, andthe second bend D with the aid of a second roof prism 13 located betweenthe last element 11 of this image transport and the second eyepiece 9.The optical axes of the final portions of the principal and secondarypathways, BX' and DY, which coincide with the optical axes of revolutionof the eyepieces, are thus rendered parallel to the axis of viewing AXand define a horizontal plane.

In this example embodiment, the reflectors and the prisms are disposedat 45° to the optical axes, so that the optical bends each form a 90°angle. The pathway splitter 8 is disposed in a manner inclined to thecentral portion AB, so that the optical axis OC of the light fluxdiverted by the splitter 8 is perpendicular to the axis AB of theintensifier 2, and that the portions with axis AB and OC are in one andthe same plane perpendicular to the viewing axis AX.

The splitting of pathways, effected by dividing the light flux, can beachieved either by splitting of pupils, for example by using areflecting element on a half-pupil of the principal optical pathway, orby employing a semi-reflecting treatment or spectral band splitter,deposited on a plane plate or a splitter cube.

The plane reflectors are, for their part, produced by any techniqueknown to those skilled in the art, for example from plane plates havingundergone a reflecting treatment (metallic, dielectric or holographic),.or from half-cube prisms used in total internal reflection or havingundergone a reflecting treatment of the same type.

The optical architecture just described is embodied in such a way thatthe principal span AB of the principal optical axis is inclined by anangle of around 30° above the horizontal plane formed by the opticalaxes of the eyepieces. It is this inclination which makes it possible toclear a space sufficient to insert, under the principal optical pathwaycoupled to the first eyepiece, a second optical pathway coupled to thesecond eyepiece. This inclination thus allows the best possiblemanagement of space so as to obtain minimum bulkiness.

According to a variant embodiment of the right eyepiece pathway coupledto the right eyepiece, the roof prisms are replaced by plane reflectorsand the image transport, consisting of the three elements 6, 10 and 11,is replaced by two image transports. A first transport composed of theelements 6 and 10, which forms at the reflector 12 an intermediate imageof the screen of the intensifier, and a second transport composed of theelement 11 which recasts this image so as to deliver an erect image tothe right eyepiece 9.

Another example embodiment, illustrated in FIG. 2, in which the elementswhich are common with those of FIG. 1 are indicated with the samereference signs, is based on the use of an intensifier with imageinversion. This inversion, which corresponds to a rotation of the imageby 180° in its plane, is obtained by virtue of so-called invertingoptical fibres incorporated into the intensifier, according totechniques. Under these conditions, and in order to deliver erect imagesto the eyepieces, the plane reflector 5 of FIG. 1 is replaced by a roofpentaprism 14, the bend B then being obtained with the aid of a doublereflection at B1, and B2 so as to reverse the image, and the roof prisms12 and 13 of the secondary eyepiece pathway are replaced by two planereflectors 12' and 13' respectively.

According to a variant of this second example embodiment and in order toreduce the bulkiness, the pentaprism 14 can be replaced by a planereflector such as the reflector 5 of FIG. 1. Moreover, the imagetransport of the principal pathway, consisting of the elements 6 and 7,is computed such that the elements 6, 7 and 3 form a single eyepieceassembly of the magnifying glass type, that is to say withoutintermediate image formation and without the appearance of eye-rings.This solution becomes extremely compact since the elements 3, 6 and 7then have very reduced thickness dimensions.

The invention is not limited to the examples described and illustrated:it is possible to invert the right and left pathways with respect to thesolutions described above; it is also possible to dispose the principaloptical axis under the horizontal plane of the axes of the eyepieces,producing an optical combination of the same type, but symmetric withrespect to this plane.

We claim:
 1. Binoculars for nighttime vision including an entranceobjective conjugate with a light-intensifier tube for forming an imageof a scene from light flux originating from the scene along a viewingaxis, an intensified image next being transmitted by an image transportand by an optical splitter which partially transmits the flux bytransmission and reflection respectively on a first pathway to a firsteyepiece and on a second pathway, which is bent twice, to a secondeyepiece, the eyepieces having axes parallel to the viewing axis,characterized in that the tube and the image transport are aligned so asto constitute a principal optical pathway along a principal optical axislying in a plane perpendicular to the viewing axis and inclined withrespect to the plane of the axes of the eyepieces, in that the secondeyepiece pathway, which is bent twice and which has an axis lying in theplane perpendicular to the viewing axis and passing through the axis ofthe principal pathway.
 2. Binoculars according to claim 1, characterizedin that the image transport includes a first common optical elementlocated between the tube and the pathway splitter and two secondelements located on each of the eyepiece pathways, the pathway splitterbeing disposed between the first element and the second elements. 3.Binoculars according to claim 2, characterized in that the tube is anintensifier tube without image inversion and in that the bend of thefirst eyepiece is bent by a plane reflector.
 4. Binoculars according toclaim 3, characterized in that the flux is transmitted on the secondeyepiece pathway, with the aid of optical elements constituting a singleimage transport optically coupled to two roof prisms.
 5. Binocularsaccording to claim 3, characterized in that the flux is transmitted onthe second eyepiece pathway, with the aid of optical elementsconstituting two image transports.
 6. Binoculars according to claim 1,characterized in that the tube is an image inverting intensifier tubeand in that the flux is transmitted on the second eyepiece pathway byoptical elements constituting a single image transport optically coupledto two plane reflectors.
 7. Binoculars according to claim 6,characterized in that the optical bend is effected on the first eyepiecepathway by reflection on a roof reflector of pentaprism type. 8.Binoculars according to claim 6, characterized in that the flux istransmitted on the first eyepiece pathway with the aid of opticalelements constituting an eyepiece of the magnifying glass type fordirect transmission of the image formed by the tube.